428
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1 /* Copyright (C) 1985, 86, 87, 93, 94, 96 Free Software Foundation, Inc.
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2
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613
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3 This file is part of XEmacs.
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4
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5 XEmacs is free software; you can redistribute it and/or modify
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6 it under the terms of the GNU General Public License as published by
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7 the Free Software Foundation; either version 2, or (at your option)
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8 any later version.
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9
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10 XEmacs is distributed in the hope that it will be useful,
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428
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 GNU General Public License for more details.
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14
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15 You should have received a copy of the GNU General Public License
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16 along with XEmacs; see the file COPYING. If not, write to
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17 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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18 Boston, MA 02111-1307, USA. */
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19
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20 /* Synced with FSF 20.2 */
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21
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22 #include <config.h>
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23 #include "lisp.h"
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24
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25 #include "buffer.h"
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26 #include <paths.h>
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27
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28 #include "sysfile.h"
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29 #include "sysdir.h"
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30 #include "syspwd.h"
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31 #include "syssignal.h" /* for kill */
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32
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33 Lisp_Object Qask_user_about_supersession_threat;
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34 Lisp_Object Qask_user_about_lock;
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444
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35 int inhibit_clash_detection;
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36
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37 #ifdef CLASH_DETECTION
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38
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428
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39 /* The strategy: to lock a file FN, create a symlink .#FN in FN's
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40 directory, with link data `user@host.pid'. This avoids a single
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41 mount (== failure) point for lock files.
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42
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43 When the host in the lock data is the current host, we can check if
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44 the pid is valid with kill.
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442
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45
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46 Otherwise, we could look at a separate file that maps hostnames to
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47 reboot times to see if the remote pid can possibly be valid, since we
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48 don't want Emacs to have to communicate via pipes or sockets or
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49 whatever to other processes, either locally or remotely; rms says
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50 that's too unreliable. Hence the separate file, which could
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51 theoretically be updated by daemons running separately -- but this
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52 whole idea is unimplemented; in practice, at least in our
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53 environment, it seems such stale locks arise fairly infrequently, and
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54 Emacs' standard methods of dealing with clashes suffice.
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55
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56 We use symlinks instead of normal files because (1) they can be
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57 stored more efficiently on the filesystem, since the kernel knows
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58 they will be small, and (2) all the info about the lock can be read
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59 in a single system call (readlink). Although we could use regular
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60 files to be useful on old systems lacking symlinks, nowadays
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61 virtually all such systems are probably single-user anyway, so it
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62 didn't seem worth the complication.
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63
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64 Similarly, we don't worry about a possible 14-character limit on
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65 file names, because those are all the same systems that don't have
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66 symlinks.
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67
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68 This is compatible with the locking scheme used by Interleaf (which
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69 has contributed this implementation for Emacs), and was designed by
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70 Ethan Jacobson, Kimbo Mundy, and others.
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71
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72 --karl@cs.umb.edu/karl@hq.ileaf.com. */
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73
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442
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74 /* Note that muleization is provided by using mule-encapsulated
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75 versions of the system calls we use like symlink(), unlink(), etc... */
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76
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428
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77
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78 /* Here is the structure that stores information about a lock. */
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79
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80 typedef struct
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81 {
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82 char *user;
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83 char *host;
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647
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84 pid_t pid;
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428
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85 } lock_info_type;
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86
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87 /* When we read the info back, we might need this much more,
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88 enough for decimal representation plus null. */
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89 #define LOCK_PID_MAX (4 * sizeof (pid_t))
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428
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90
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91 /* Free the two dynamically-allocated pieces in PTR. */
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92 #define FREE_LOCK_INFO(i) do { xfree ((i).user); xfree ((i).host); } while (0)
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93
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94 /* Write the name of the lock file for FN into LFNAME. Length will be
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95 that of FN plus two more for the leading `.#' plus one for the null. */
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96 #define MAKE_LOCK_NAME(lock, file) \
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442
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97 (lock = (char *) alloca (XSTRING_LENGTH (file) + 2 + 1), \
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665
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98 fill_in_lock_file_name ((Intbyte *) (lock), (file)))
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428
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99
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100 static void
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665
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101 fill_in_lock_file_name (Intbyte *lockfile, Lisp_Object fn)
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428
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102 {
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665
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103 Intbyte *file_name = XSTRING_DATA (fn);
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104 Intbyte *p;
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647
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105 Bytecount dirlen;
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428
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106
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442
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107 for (p = file_name + XSTRING_LENGTH (fn) - 1;
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108 p > file_name && !IS_ANY_SEP (p[-1]);
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109 p--)
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110 ;
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111 dirlen = p - file_name;
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112
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442
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113 memcpy (lockfile, file_name, dirlen);
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114 p = lockfile + dirlen;
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115 *(p++) = '.';
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116 *(p++) = '#';
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117 memcpy (p, file_name + dirlen, XSTRING_LENGTH (fn) - dirlen + 1);
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428
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118 }
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119
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120 /* Lock the lock file named LFNAME.
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121 If FORCE is nonzero, we do so even if it is already locked.
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122 Return 1 if successful, 0 if not. */
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123
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124 static int
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442
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125 lock_file_1 (char *lfname, int force)
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428
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126 {
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442
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127 /* Does not GC. */
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128 int err;
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129 char *lock_info_str;
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428
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130 char *host_name;
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442
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131 char *user_name = user_login_name (NULL);
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428
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132
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442
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133 if (user_name == NULL)
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428
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134 user_name = "";
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442
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135
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136 if (STRINGP (Vsystem_name))
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137 host_name = (char *) XSTRING_DATA (Vsystem_name);
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428
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138 else
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139 host_name = "";
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442
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140
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428
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141 lock_info_str = (char *)alloca (strlen (user_name) + strlen (host_name)
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142 + LOCK_PID_MAX + 5);
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143
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647
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144 sprintf (lock_info_str, "%s@%s.%d", user_name, host_name, getpid ());
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428
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145
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146 err = symlink (lock_info_str, lfname);
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147 if (err != 0 && errno == EEXIST && force)
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428
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148 {
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149 unlink (lfname);
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150 err = symlink (lock_info_str, lfname);
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151 }
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152
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153 return err == 0;
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154 }
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155
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156 /* Return 0 if nobody owns the lock file LFNAME or the lock is obsolete,
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157 1 if another process owns it (and set OWNER (if non-null) to info),
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158 2 if the current process owns it,
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159 or -1 if something is wrong with the locking mechanism. */
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160
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161 static int
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162 current_lock_owner (lock_info_type *owner, char *lfname)
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163 {
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442
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164 /* Does not GC. */
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165 int len, ret;
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428
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166 int local_owner = 0;
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167 char *at, *dot;
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168 char *lfinfo = 0;
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169 int bufsize = 50;
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170 /* Read arbitrarily-long contents of symlink. Similar code in
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171 file-symlink-p in fileio.c. */
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172 do
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173 {
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174 bufsize *= 2;
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175 lfinfo = (char *) xrealloc (lfinfo, bufsize);
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176 len = readlink (lfname, lfinfo, bufsize);
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177 }
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178 while (len >= bufsize);
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442
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179
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428
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180 /* If nonexistent lock file, all is well; otherwise, got strange error. */
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181 if (len == -1)
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182 {
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183 xfree (lfinfo);
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184 return errno == ENOENT ? 0 : -1;
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185 }
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186
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187 /* Link info exists, so `len' is its length. Null terminate. */
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188 lfinfo[len] = 0;
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189
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428
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190 /* Even if the caller doesn't want the owner info, we still have to
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191 read it to determine return value, so allocate it. */
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192 if (!owner)
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193 {
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194 owner = (lock_info_type *) alloca (sizeof (lock_info_type));
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195 local_owner = 1;
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196 }
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442
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197
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428
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198 /* Parse USER@HOST.PID. If can't parse, return -1. */
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199 /* The USER is everything before the first @. */
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200 at = strchr (lfinfo, '@');
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201 dot = strrchr (lfinfo, '.');
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202 if (!at || !dot) {
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203 xfree (lfinfo);
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204 return -1;
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205 }
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206 len = at - lfinfo;
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207 owner->user = (char *) xmalloc (len + 1);
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208 strncpy (owner->user, lfinfo, len);
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209 owner->user[len] = 0;
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442
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210
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428
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211 /* The PID is everything after the last `.'. */
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212 owner->pid = atoi (dot + 1);
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213
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214 /* The host is everything in between. */
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215 len = dot - at - 1;
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216 owner->host = (char *) xmalloc (len + 1);
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217 strncpy (owner->host, at + 1, len);
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218 owner->host[len] = 0;
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219
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220 /* We're done looking at the link info. */
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221 xfree (lfinfo);
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442
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222
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428
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223 /* On current host? */
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442
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224 if (STRINGP (Fsystem_name ())
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225 && strcmp (owner->host, (char *) XSTRING_DATA (Fsystem_name ())) == 0)
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428
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226 {
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227 if (owner->pid == getpid ())
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228 ret = 2; /* We own it. */
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229 else if (owner->pid > 0
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230 && (kill (owner->pid, 0) >= 0 || errno == EPERM))
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231 ret = 1; /* An existing process on this machine owns it. */
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232 /* The owner process is dead or has a strange pid (<=0), so try to
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233 zap the lockfile. */
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234 else if (unlink (lfname) < 0)
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235 ret = -1;
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236 else
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237 ret = 0;
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238 }
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239 else
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240 { /* If we wanted to support the check for stale locks on remote machines,
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241 here's where we'd do it. */
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242 ret = 1;
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243 }
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442
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244
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428
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245 /* Avoid garbage. */
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246 if (local_owner || ret <= 0)
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247 {
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248 FREE_LOCK_INFO (*owner);
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249 }
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250 return ret;
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251 }
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252
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253 /* Lock the lock named LFNAME if possible.
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254 Return 0 in that case.
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255 Return positive if some other process owns the lock, and info about
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256 that process in CLASHER.
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257 Return -1 if cannot lock for any other reason. */
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258
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259 static int
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260 lock_if_free (lock_info_type *clasher, char *lfname)
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261 {
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442
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262 /* Does not GC. */
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428
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263 if (lock_file_1 (lfname, 0) == 0)
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264 {
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265 int locker;
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266
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267 if (errno != EEXIST)
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268 return -1;
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442
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269
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428
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270 locker = current_lock_owner (clasher, lfname);
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271 if (locker == 2)
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272 {
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273 FREE_LOCK_INFO (*clasher);
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274 return 0; /* We ourselves locked it. */
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275 }
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276 else if (locker == 1)
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277 return 1; /* Someone else has it. */
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278
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279 return -1; /* Something's wrong. */
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280 }
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281 return 0;
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282 }
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283
|
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284 /* lock_file locks file FN,
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285 meaning it serves notice on the world that you intend to edit that file.
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286 This should be done only when about to modify a file-visiting
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287 buffer previously unmodified.
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288 Do not (normally) call this for a buffer already modified,
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289 as either the file is already locked, or the user has already
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290 decided to go ahead without locking.
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291
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292 When this returns, either the lock is locked for us,
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293 or the user has said to go ahead without locking.
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294
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295 If the file is locked by someone else, this calls
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296 ask-user-about-lock (a Lisp function) with two arguments,
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297 the file name and info about the user who did the locking.
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298 This function can signal an error, or return t meaning
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299 take away the lock, or return nil meaning ignore the lock. */
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300
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301 void
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302 lock_file (Lisp_Object fn)
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303 {
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442
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304 /* This function can GC. GC checked 7-11-00 ben */
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428
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305 /* dmoore - and can destroy current_buffer and all sorts of other
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306 mean nasty things with pointy teeth. If you call this make sure
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307 you protect things right. */
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442
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308 /* Somebody updated the code in this function and removed the previous
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428
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309 comment. -slb */
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310
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311 register Lisp_Object attack, orig_fn;
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312 register char *lfname, *locker;
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313 lock_info_type lock_info;
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444
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314 struct gcpro gcpro1, gcpro2, gcpro3;
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315 Lisp_Object old_current_buffer;
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428
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316 Lisp_Object subject_buf;
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317
|
444
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318 if (inhibit_clash_detection)
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319 return;
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320
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321 XSETBUFFER (old_current_buffer, current_buffer);
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446
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322 subject_buf = Qnil;
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444
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323 GCPRO3 (fn, subject_buf, old_current_buffer);
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428
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324 orig_fn = fn;
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325 fn = Fexpand_file_name (fn, Qnil);
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326
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327 /* Create the name of the lock-file for file fn */
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328 MAKE_LOCK_NAME (lfname, fn);
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329
|
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330 /* See if this file is visited and has changed on disk since it was
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331 visited. */
|
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332 {
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333 subject_buf = get_truename_buffer (orig_fn);
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334 if (!NILP (subject_buf)
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335 && NILP (Fverify_visited_file_modtime (subject_buf))
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336 && !NILP (Ffile_exists_p (fn)))
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442
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337 call1_in_buffer (XBUFFER (subject_buf),
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338 Qask_user_about_supersession_threat, fn);
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428
|
339 }
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340
|
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341 /* Try to lock the lock. */
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444
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342 if (current_buffer != XBUFFER (old_current_buffer)
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343 || lock_if_free (&lock_info, lfname) <= 0)
|
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344 /* Return now if we have locked it, or if lock creation failed
|
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345 or current buffer is killed. */
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428
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346 goto done;
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347
|
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348 /* Else consider breaking the lock */
|
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349 locker = (char *) alloca (strlen (lock_info.user) + strlen (lock_info.host)
|
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350 + LOCK_PID_MAX + 9);
|
647
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351 sprintf (locker, "%s@%s (pid %d)", lock_info.user, lock_info.host,
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428
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352 lock_info.pid);
|
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353 FREE_LOCK_INFO (lock_info);
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442
|
354
|
428
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355 attack = call2_in_buffer (BUFFERP (subject_buf) ? XBUFFER (subject_buf) :
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356 current_buffer, Qask_user_about_lock , fn,
|
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357 build_string (locker));
|
444
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358 if (!NILP (attack) && current_buffer == XBUFFER (old_current_buffer))
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428
|
359 /* User says take the lock */
|
|
360 {
|
|
361 lock_file_1 (lfname, 1);
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362 goto done;
|
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363 }
|
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364 /* User says ignore the lock */
|
|
365 done:
|
|
366 UNGCPRO;
|
|
367 }
|
|
368
|
|
369 void
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|
370 unlock_file (Lisp_Object fn)
|
|
371 {
|
442
|
372 /* This can GC */
|
428
|
373 register char *lfname;
|
442
|
374 struct gcpro gcpro1;
|
|
375
|
|
376 GCPRO1 (fn);
|
428
|
377
|
|
378 fn = Fexpand_file_name (fn, Qnil);
|
|
379
|
|
380 MAKE_LOCK_NAME (lfname, fn);
|
|
381
|
|
382 if (current_lock_owner (0, lfname) == 2)
|
|
383 unlink (lfname);
|
442
|
384
|
|
385 UNGCPRO;
|
428
|
386 }
|
|
387
|
|
388 void
|
442
|
389 unlock_all_files (void)
|
428
|
390 {
|
|
391 register Lisp_Object tail;
|
|
392
|
434
|
393 for (tail = Vbuffer_alist; CONSP (tail); tail = XCDR (tail))
|
428
|
394 {
|
442
|
395 struct buffer *b = XBUFFER (XCDR (XCAR (tail)));
|
428
|
396 if (STRINGP (b->file_truename) && BUF_SAVE_MODIFF (b) < BUF_MODIFF (b))
|
|
397 unlock_file (b->file_truename);
|
|
398 }
|
|
399 }
|
|
400
|
|
401 DEFUN ("lock-buffer", Flock_buffer, 0, 1, 0, /*
|
442
|
402 Lock FILE, if current buffer is modified.
|
|
403 FILE defaults to current buffer's visited file,
|
428
|
404 or else nothing is done if current buffer isn't visiting a file.
|
|
405 */
|
442
|
406 (file))
|
428
|
407 {
|
|
408 if (NILP (file))
|
|
409 file = current_buffer->file_truename;
|
|
410 CHECK_STRING (file);
|
|
411 if (BUF_SAVE_MODIFF (current_buffer) < BUF_MODIFF (current_buffer)
|
|
412 && !NILP (file))
|
|
413 lock_file (file);
|
|
414 return Qnil;
|
|
415 }
|
|
416
|
|
417 DEFUN ("unlock-buffer", Funlock_buffer, 0, 0, 0, /*
|
|
418 Unlock the file visited in the current buffer,
|
|
419 if it should normally be locked.
|
|
420 */
|
|
421 ())
|
|
422 {
|
|
423 /* This function can GC */
|
|
424 /* dmoore - and can destroy current_buffer and all sorts of other
|
|
425 mean nasty things with pointy teeth. If you call this make sure
|
|
426 you protect things right. */
|
|
427
|
|
428 if (BUF_SAVE_MODIFF (current_buffer) < BUF_MODIFF (current_buffer)
|
|
429 && STRINGP (current_buffer->file_truename))
|
|
430 unlock_file (current_buffer->file_truename);
|
|
431 return Qnil;
|
|
432 }
|
|
433
|
|
434 /* Unlock the file visited in buffer BUFFER. */
|
|
435
|
|
436
|
|
437 void
|
|
438 unlock_buffer (struct buffer *buffer)
|
|
439 {
|
|
440 /* This function can GC */
|
|
441 /* dmoore - and can destroy current_buffer and all sorts of other
|
|
442 mean nasty things with pointy teeth. If you call this make sure
|
|
443 you protect things right. */
|
|
444 if (BUF_SAVE_MODIFF (buffer) < BUF_MODIFF (buffer)
|
|
445 && STRINGP (buffer->file_truename))
|
|
446 unlock_file (buffer->file_truename);
|
|
447 }
|
|
448
|
|
449 DEFUN ("file-locked-p", Ffile_locked_p, 0, 1, 0, /*
|
442
|
450 Return nil if the FILENAME is not locked,
|
428
|
451 t if it is locked by you, else a string of the name of the locker.
|
|
452 */
|
442
|
453 (filename))
|
428
|
454 {
|
|
455 Lisp_Object ret;
|
|
456 register char *lfname;
|
|
457 int owner;
|
|
458 lock_info_type locker;
|
442
|
459 struct gcpro gcpro1;
|
|
460
|
|
461 GCPRO1 (filename);
|
428
|
462
|
|
463 filename = Fexpand_file_name (filename, Qnil);
|
|
464
|
|
465 MAKE_LOCK_NAME (lfname, filename);
|
|
466
|
|
467 owner = current_lock_owner (&locker, lfname);
|
|
468 if (owner <= 0)
|
|
469 ret = Qnil;
|
|
470 else if (owner == 2)
|
|
471 ret = Qt;
|
|
472 else
|
|
473 ret = build_string (locker.user);
|
|
474
|
|
475 if (owner > 0)
|
|
476 FREE_LOCK_INFO (locker);
|
|
477
|
442
|
478 UNGCPRO;
|
|
479
|
428
|
480 return ret;
|
|
481 }
|
|
482
|
|
483
|
|
484 /* Initialization functions. */
|
|
485
|
|
486 void
|
|
487 syms_of_filelock (void)
|
|
488 {
|
|
489 /* This function can GC */
|
|
490 DEFSUBR (Funlock_buffer);
|
|
491 DEFSUBR (Flock_buffer);
|
|
492 DEFSUBR (Ffile_locked_p);
|
|
493
|
563
|
494 DEFSYMBOL (Qask_user_about_supersession_threat);
|
|
495 DEFSYMBOL (Qask_user_about_lock);
|
428
|
496 }
|
|
497
|
444
|
498 void
|
|
499 vars_of_filelock (void)
|
|
500 {
|
|
501 DEFVAR_BOOL ("inhibit-clash-detection", &inhibit_clash_detection /*
|
|
502 Non-nil inhibits creation of lock file to detect clash.
|
|
503 */);
|
|
504 inhibit_clash_detection = 0;
|
|
505 }
|
428
|
506
|
|
507 #endif /* CLASH_DETECTION */
|